The invention relates to a high voltage quick-break fuse with at least one silver fuse element and at least one tin fuse element in series connection, the silver fuse element being notched or perforated at intervals to influence its characteristics and the tin fuse element being surrounded by an arc-quenching or extinguishing material.
Such fuses are intended to break both extreme short-circuit currents and also overload currents only slightly above the rated current, so that they are also referred to as full-range fuses. More particularly as a result of the chosen melting point for the two series-connected fuse elements or fuse element groups, the tin fuse element is responsible for quenching under relatively low overcurrents, whilst the silver fuse element responds under extreme short-circuit currents (German Pat. No. 24 12 688). One of the most important requirements for a full-range fuse is that it brings about the break or interruption without any explosion-like self-destruction, i.e. undergoes no external changes.
It has been found that although the hitherto proposed fuses operate satisfactorily in the top and bottom overcurrent range, in a median range both fuse elements or fuse element groups react to the overcurrent, without the desired break taking place prior to an explosion. This process briefly takes place in the following way. The critical overcurrent is not sufficient to evaporate the tin fuse element in a more or less instantaneous manner, or to produce a large interruption point by fusing. Within the silver fuse element, the overcurrent is also not sufficient to produce an adequately large interruption to bring about a breaking process, so that the silver fuse element is initially only opened in the vicinity of a single constriction, which is formed by notches or a perforation. A stationary arc is formed at this point, which starts to melt and carbonize the surrounding sand filling, so that in spite of the interruption of the silver fuse element, this point is permanently conductive. This process is continued and it must be borne in mind that a powerful arc is present throughout this period. Before the tin fuse element, due to its slow response, finally brings about a separation, the arc emanating from the vicinity of the silver fuse element has often attacked and decomposed the quenching sleeve of the tin fuse element to such an extent that an interruption of the current in the tin/silicone system is no longer possible, and due to the internal pressure within the fuse, the latter explodes. Thus, as a result of the destructive action from the area of the silver fuse element, the separating action from the area of the tin fuse element comes too late to protect the fuse against explosion.